The invention relates to a method of and an arrangement for controlling the rotational and translatory motions of a manipulator or industrial robot, which automatically for the entire motion and speed range even in the event of a simultaneous movement of a plurality of motion actuators permit uniform, selectible and defect-independent dynamic control properties for individual or all motion variables.
For controlling motion variables (such as angle of rotation and extension lengths) of manipulators and industrial robots in relationship to predetermined values or predetermined trajectories, it is necessary that a substantial constancy of the dynamic control properties for all duty ranges and operational conditions be achieved without any readjustment of control parameters being necessary manually. A manual readjustment is not possible anyhow in practical use because of the rapidly changing work motions, and the same applies accordingly for the use of manipulators or robots in non-accessible areas such as for instance in nuclear engineering, in space engineering or in general areas of danger. The constancy of the dynamic control properties under various operational conditions is of great significance for the use of a manipulation system because, for instance, for assembly tasks an overswinging beyond the predetermined position may result in damage to the robot arm or in knocking down of the workpiece or tool to be gripped. A further example for the necessity of this requirement is that in the coordinated operation of two or more motion parameters of the roboter for following a predetermined trajectory the time behavior of the controlling of each individual motion variable must be identical, since otherwise track deviations occur which may result in an inaccurate work performance or in the arm colliding with an obstruction. Insuring constancy of the dynamic control properties is of particular significance for higher work speeds of the manipulator or industrial robot (equal to or greater than human motion speed) and for simultaneous higher standards of accuracy. Both objectives are strived for in the development of industrial robots and manipulators, in order to permit an economical use, for instance in the finishing technique. These objectives are also goal-leading for the use in manipulation tasks to be performed rapidly and precisely in non-accessible areas such as nuclear engineering and space engineering or in all types of areas of danger.
For the operation of manipulators and industrial robots, systems are known which receive the predetermined values of the motion variables in various types of stores (such as punched cards, magnetic tapes, etc.) and perform the motion course through the intermediary of a control. Prior art furthermore includes control methods for manipulators and industrial robots which are substantially identical with the control methods for machine tools, and use simple control loops with a PID behaviour for the preset-actual value control of the individual motion variables. A survey of the present state of the art of manipulators and industrial robots is presented in the "Erfahrungsaustausch Industrieroboter 1975", 5th Work Meeting, Institut fur Produktionstechnik und Automatisierung (IPA) of the Fraunhofer Gesellschaft e.V. of the University of Stuttgart.
The conventional control arrangements for robot systems with PID controllers are insufficient for higher requirements to be provided regarding motion speed and accuracy. For work speeds in the range of human motion speed or higher speeds the dynamic intercouplings of each individual motion parameter to be controlled by the other motions of the manipulator or robot (for instance by centrifugal force or Coriolis-force) become so high that an error adjustment for the interferences by the PID controller is not possible within the period of time required for practical operations. These interference signals have been found to be a multiple of the actual control signal which would be generated without such dynamic intercouplings. Investigations with manipulators having more than three degrees of freedom have shown for higher standards of speed and accuracy that in these instances control with PID controllers is not possible any more for technically reasonable requirements for the reasons indicated. A further difficulty with a PID control is that the inertia moments to be accelerated have been found to vary up to a ratio of 1 to 10 during the course of movement. This for instance happens by retracting a rotating arm or by placing two arms behind each other by bending an arm. This means that the same positioning signal and thus positioning moment of the motor which is supplied from the control system acts upon a materially varying moment of inertia. This results in very different dynamics of the course of movement. The same applies accordingly in the correlated scope for a varied load of the gripper. Conventional control arrangements or manipulators and industrial robots therefore do not fulfill the mentioned requirements regarding work speed and simultaneous accuracy.